John Jackson was His Majesty’s Astronomer at the Royal Observatory, Cape of Good Hope.

Jackson was the fifth of eight children born to Matthew and Jeannie (née Millar) Jackson. He entered Glasgow University at the age of 16 and graduated with an MA in mathematics (1907), followed by a BSc (1908) with special distinction in mathematics, natural philosophy, astronomy, and chemistry. Jackson then went to Cambridge University, where he obtained a first class degree in the mathematical tripos. His first research concerned the motion of the eighth satellite of Jupiter, which had been discovered by Phillibert Melotte at Greenwich in 1908.

In 1914, Jackson was appointed chief assistant at the Royal Observatory, Greenwich. He did much routine observing during World War I, especially with the Airy Transit Circle. In 1917, Jackson was commissioned in the Royal Engineers. He was sent to France as a trigonometric...